The objective of this research is the evaluation of the dynamic properties of the membranes of cardiac muscle cells and autonomic nerve cells (sympathetic adrenergic efferent fibers) during development of the avian heart. Intracellular microelectrode recording techniques will provide quantitative information about the electrical activity of individual cardiac cells during growth and development of the chick embryo. Exaamination of the changes of intracellular membrane potentials (particularly the Ca-de endent slow channel action potential) along with measurements of cellular cyclic AMP content and of developed tension will assist in our understanding of the regulation of ion transport and the maintenance of cellular homeostasis. Drugs (particularly those related to the sympathetic adrenergic nervous system) will be used as probes of embryonic heart membranes. Alterations in reactivity of electrical, chemical and mechanical parameters to drugs will serve as indices of ontogenetic changes that occur in the mechanism regulated by drug-receptor interaction. The role of the adrenergic neuron in modulating intrinsic cardiac activity and membrane sensitivity to beta-adrenergic agonists will be examined in aneural and innervated hearts. In addition, the sympathetic adrenergic innervation will be modified by treatment of animals with nerve growth factor (NGF), anti-N0F and 6-hydroxydopamine. The histochemical features of adrenergic neuron distribution will be compared with the neurosecretory properties of the developing adrenergic neuron. Neurosecretion will be measured by studying the release of 3H-norepinephrine from intracardiac nerves. This study can provide a better understanding of synaptogenesis and its effects on cardiac function during a critical biological period.